Strongly improved performance of calculating the bounding boxes

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
The multiply operator now draws a dot instead of an X

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Improved the performance when calculating bounding boxes in MathOperationDivide

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Optimized the bounding box calculation for MathOperationPower
Also made it so that it's always positioned right.

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Improved the bounding box calculation of MathConstant
* The constants are now drawn as they should
* Fixed some bugs in evaluating, approximating and parsing constants
- Removed some unnecessary variables from MathConstant

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Added the icon  the designer made

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Fixed a bug where an invalid text size would be returned by MathConstant's findTextSize()

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
The MathView now draws an empty box when there is no MathObject associated with it

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>